In a hybrid automatic repeat request (Hybrid Automatic Repeat Request, HARQ) technology, a data receiver needs to feed back acknowledgement information to a data transmitter to help the data transmitter confirm whether data is received correctly. Usually, an acknowledgement (Acknowledgement, ACK) is used to indicate correct reception, and a negative acknowledgement (Negative-acknowledgement, NACK) is used to indicate incorrect reception. The acknowledgement information may also be called ACK/NACK feedback information. In an uplink (Uplink, UL) direction of a 3rd Generation Partnership Project (3rd Generation Partnership Project, 3GPP) evolved universal terrestrial radio access (Evolved Universal Terrestrial Radio Access, E-UTRA) system, a user equipment feeds back acknowledgement information of downlink data reception to a base station through a physical uplink control channel (Physical Uplink Control Channel, PUCCH). The 3GPP E-UTRA system is also called a long term evolution (Long Term Evolution, LTE) system.
In an LTE-advanced (LTE-Advanced, LTE-A) system, a carrier aggregation technology is selected to be used for supporting wider bandwidth, so as to satisfy the requirement of the International Telecommunication Union for the peak data rate of a fourth generation communication technology. In the carrier aggregation technology, spectrums of two or more component carriers are aggregated to obtain wider transmission bandwidth. For a user equipment of the LTE-A, different quantities of uplink carriers and component carriers may be configured, and each component carrier has an independent HARQ process. When the user equipment of the LTE-A accesses multiple component carriers simultaneously, corresponding acknowledgement information needs to be fed back with respect to the data transmitted on a physical downlink shared channel (Physical Downlink Shared Channel, PDSCH) of each component carrier to the user equipment or downlink control information (Downlink Control Information, DCI) indicating downlink semi-persistent scheduling (Semi-Persistent Scheduling, SPS) release. Furthermore, the acknowledgement information corresponding to the multiple component carriers needs to be fed back in the same uplink component carrier.
In a time division duplex (Time Division Duplexing, TDD) system having multiple component carriers, there is only the concept of component carriers and there is no definite concept of uplink component carriers and downlink component carriers, because both uplink transmission and downlink transmission occur on a same frequency band, that is, each component carrier has both uplink transmission and downlink transmission, to be specific, each component carrier serves as both an uplink component carrier and a downlink component carrier. The uplink transmission and downlink transmission are segmented and staggered only in units of subframes according to time, that is, some subframes are used for downlink transmission and are called downlink subframes (Downlink subframe), and some subframes are used for uplink transmission and are called uplink subframes (Uplink subframe). In addition, there are multiple possible uplink and downlink segmentation modes, and therefore, the number of uplink subframes may be asymmetric to the number of downlink subframes, that is, acknowledgement information corresponding to data transmission on multiple downlink subframes needs to be fed back on a same uplink subframe. That is, feeding back, by the component carrier used for uplink feedback of acknowledgement information, acknowledgement information of downlink subframes on the multiple component carriers, includes: feeding back acknowledgement information corresponding to the data transmission on multiple downlink subframes on each component carrier.
The uplink/downlink subframe configuration in LTE/LTE-A TDD is shown in Table 1, where ‘D’ indicates a downlink subframe, ‘U’ indicates an uplink subframe, and ‘S’ indicates a special subframe, where the special subframe is also mainly used for downlink transmission.
TABLE 1Uplink/Down- link Subframe RepetitionSubframe NumberConfigurationPeriod01 2345 67890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD6 5 msDSUUUDSUUD
During acknowledgement information feedback, for a subframe position of a carrier on which no actual data is transmitted to a user, the user sets several acknowledgement information bits corresponding to the position to preset values during feedback. For example, for the subframe on which no actual data is transmitted to the user, the values of corresponding acknowledgement information bits are set to ‘0’. However, data is transmitted by the base station to the user, and the user equipment further needs to consume resources (such as power) to feed back the acknowledgement information that is known to the base station and is unnecessary to be fed back, resulting in waste of transmit power and performance loss of the user equipment.